LED control device for phase-cut dimming system and control method thereof

ABSTRACT

An LED control device for configuring a phase-cut dimming system includes an LED and a switch. The LED control device configures the conduction status of the switch so as to supply power to the LED according to an input signal. The LED control device further detects whether the input signal is phase-cut. When the input signal is phase-cut, the LED control device stores the signal values of the internal circuits. Afterward, when the input signal is not phase-cut, the LED control device restores the stored signal values so that the internal circuits may resume to the previous operation status rapidly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Patent ApplicationNo. 101122581, filed in Taiwan on Jun. 25, 2012; the entirety of whichis incorporated herein by reference for all purposes.

BACKGROUND

The disclosure generally relates to an LED control device and, moreparticularly, to the LED control device utilized in the phase-cutdimming system.

The LEDs (light emitting diodes) have the advantages of high luminousefficacy, long product life, compact dimensions, fast startup time, highreliability, high durability, etc. More and more people have replacedthe traditional light sources with LEDs in the indoor and the outdoorenvironment, e.g., the house, the office, the billboard and thestreetlamps.

The LEDs, however, may malfunction when cooperating with traditionalcircuits or control devices. For example, many traditional light sourcesmay cooperate with the phase-cut dimming circuit for adjusting thebrightness of the light sources. The phase-cut dimming circuit maycomprise the TRIAC (triode for alternating current), the diode or othersuitable circuit elements for cutting off part of the AC input signal sothat the brightness of the light sources may be adjusted accordingly.When the AC input signal is cut off, the voltage or the current of theAC input signal is configured to be zero or a small value. In thisfield, the conduction angle is known as 180 degrees minus the anglecorresponding to the cut-off portion of the AC input signal. Forexample, when the AC input signal is not cut off at all, the conductionangle is 180 degrees. When the AC input signal is completely cut off,the conduction angle is 0 degree.

Moreover, the LED control device is needed to drive the LEDs, stabilizethe voltage, stabilize the current, adjust the power factor, etc. TheLED control device, however, causes problems when adjusting thebrightness of the LED in the phase-cut dimming system. For example, whenthe phase-cut portion of the AC input signal is too small (i.e., theconduction angle is large), the LED control device will perform thecompensation operation to stabilize the voltage and/or the current. Whenthe conduction angle is large, the voltage and/or the current suppliedto the LED almost do not vary because of the compensation operations ofthe LED control device, and the brightness of the LED cannot beadjusted. Therefore, when the conduction angle is large, the dimmingfunction cannot be performed correctly. The dimming linearity of the LEDdimming system is affected, and the user cannot easily adjust the LED tothe desired brightness.

Moreover, there are also other problems when the phase-cut dimmercooperates with the LED to perform the dimming function. For example,when the AC input signal is phase-cut, the LED control device is notpowered. Afterward, when the AC input signal is no longer phase-cut,some circuits in the LED control device will be restarted. In the periodof restarting the circuits, the voltage and/or the current supplied tothe LED usually differ from the value(s) before the AC input signal isphase-cut. Therefore, the dimming linearity of the LED dimming system isalso affected, and the LED may even flicker. The users would notice andfeel uncomfortable when the LED flickers in the phase-cut dimmingsystem.

SUMMARY

In view of the foregoing, it may be appreciated that a substantial needexists for methods and apparatuses that mitigate or reduce the problemsabove.

An example embodiment of an LED control device for configuring aphase-cut dimming system according to a input signal; wherein thephase-cut dimming system comprises an LED and a current switch;comprising: a current control circuit for coupling with the currentswitch, and for generating a second output signal according to a currentflowing through the current switch; a driving signal generating circuitfor coupling with a control terminal of the current switch and thecurrent control circuit, and for generating a driving signal toconfigure a conduction status of the current switch according to thesecond output signal and a periodic signal; and a phase-cut detectioncircuit for receiving the input signal, and for comparing the inputsignal with a second reference signal; wherein in a first period inwhich the input signal is greater than the second reference signal, thephase-cut detection circuit configures a signal value of a secondstorage device to vary with the second output signal; in a second periodin which the input signal is less than the second reference signal, thephase-cut detection circuit configures the second storage device to keepthe signal value of the second storage device so as not to vary with thesecond output signal; in a third period in which the input signal isgreater than the second reference signal, the phase-cut detectioncircuit configures the signal value of the second storage device to varywith the second output signal; and the second storage device isconfigured to be operably coupled with the current control circuit andthe driving signal generating circuit.

Another example embodiment of an LED control device for configuring aphase-cut dimming system according to a input signal; wherein thephase-cut dimming system comprises an LED and a current switch, and acurrent flowing through the current switch flows through a resistor togenerate a detection voltage signal; comprising: a current controlcircuit for coupling with the current switch, and for generating asecond output signal according to the current flowing through thecurrent switch; a driving signal generating circuit for coupling with acontrol terminal of the current switch and the current control circuit,and for generating a driving signal to configure a conduction status ofthe current switch according to the second output signal and a periodicsignal; and a phase-cut detection circuit for receiving the detectionvoltage signal, and for comparing the detection voltage signal with athird reference signal; wherein in a first period in which the detectionvoltage signal is greater than the third reference signal, the phase-cutdetection circuit configures a signal value of a second storage deviceto vary with the second output signal; in a second period in which thedetection voltage signal is less than the third reference signal, thephase-cut detection circuit configures the second storage device to keepthe signal value of the second storage device so as not to vary with thesecond output signal; in a third period in which the detection voltagesignal is greater than the third reference signal, the phase-cutdetection circuit configures the signal value of a second storage deviceto vary with the second output signal; and the second storage device isconfigured to be operably coupled with the current control circuit andthe driving signal generating circuit.

Another example embodiment of a control method for configuring aphase-cut dimming system according to a input signal; wherein thephase-cut dimming system comprises an LED and a current switch;comprising: generating a second output signal according to a currentflowing through the current switch; generating a driving signal toconfigure a conduction status of the current switch according to thesecond output signal and a periodic signal; and in a first period inwhich the input signal is not phase-cut, configuring a signal value of asecond storage device to vary with the second output signal; in a secondperiod in which the input signal is phase-cut, configuring the secondstorage device to keep the signal value of the second storage device soas not to vary with the second output signal; and in a third period inwhich the input signal is not phase-cut, configuring the signal value ofthe second storage device to vary with the second output signal.

Another example embodiment of a control method for configuring aphase-cut dimming system according to a input signal; wherein thephase-cut dimming system comprises an LED and a current switch and acurrent switch, and a current flowing through the current switch flowsthrough a resistor to generate a detection voltage signal; comprising:generating a second output signal according to a current flowing throughthe current switch; generating a driving signal to configure aconduction status of the current switch according to the second outputsignal and a periodic signal; and comparing the detection voltage signalwith a third reference signal to determine whether the input signal isphase-cut; in a first period in which the input signal is not phase-cut,configuring a signal value of a second storage device to vary with thesecond output signal; in a second period in which the input signal isphase-cut, configuring the second storage device to keep the signalvalue of the second storage device so as not to vary with the secondoutput signal; and in a third period in which the input signal is notphase-cut, configuring the signal value of the second storage device tovary with the second output signal.

Both the foregoing general description and the following detaileddescription are examples and explanatory only, and are not restrictiveof the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified functional block diagram of a phase-cutdimming system according to one embodiment of the present disclosure.

FIG. 2 shows simplified waveforms of the AC input signal and severalphase-cut signals of the phase-cut dimming system in FIG. 1.

FIG. 3 shows a simplified functional block diagram of the LED controldevice of the phase-cut dimming system in FIG. 1 according to oneembodiment of the present disclosure.

FIG. 4 shows simplified waveforms of several signals of the phase-cutdimming system in FIG. 1.

FIG. 5 shows a simplified functional block diagram of a phase-cutdimming system according to another embodiment of the presentdisclosure.

FIG. 6 shows a simplified functional block diagram of the LED controldevice of the phase-cut dimming system in FIG. 5 according to oneembodiment of the present disclosure.

FIG. 7 shows a simplified functional block diagram of a phase-cutdimming system according to another embodiment of the presentdisclosure.

DETAILED DESCRIPTION

Reference is made in detail to embodiments of the invention, which areillustrated in the accompanying drawings. The same reference numbers maybe used throughout the drawings to refer to the same or like parts,components, or operations.

FIG. 1 shows a simplified functional block diagram of a phase-cutdimming system 100 according to one embodiment of the presentdisclosure. The phase-cut dimming system 100 comprises a phase-cutdimmer 110, a transformer 120, a group of LEDs 130, a voltage dividingcircuit 140, a current switch 150, a resistor 160 and a LED controldevice 170. For the purposes of conciseness and clear explanation, somecomponents, signals and connections thereof are not shown in FIG. 1. Forexample, the protection circuit for the LEDs 130 and some impedancecircuit elements are not shown in FIG. 1.

The phase-cut dimmer 110 is coupled with the AC power source to receivethe AC input signal Vac and to generate the corresponding input signalVin. The phase-cut dimmer 110 may generate the input signal Vin with aphase-cut portion configured by the user. For example, the user mayconfigure the phase-cut portion of the AC input signal Vac by turning aknob or moving a slide bar (not shown in FIG. 1) of the phase-cutdimmer. In this embodiment, the phase-cut dimmer 100 further comprisesthe circuit to perform the full wave rectification function forgenerating the input signal Vin according to the AC input signal Vac.

FIG. 2 shows simplified waveforms of the AC input signal Vac and severalphase-cut signals of the phase-cut dimming system 100 in FIG. 1. In thisembodiment, the AC input signal Vac is a sinusoidal signal and expressedas Vac=A1*sin(ωt) wherein A1 and ω are respectively the amplitude andthe angular frequency of the AC input signal Vac. The phase-cut dimmer110 may be configured to generate the input signal Vin with the requiredphase-cut portion. For example, in FIG. 2, the input signal Vin1 is asignal without being phase-cut (i.e., the conduction angle of the inputsignal Vin1 is 180 degrees). The input signal Vin2 is a signal with thesignal being completely phase-cut (i.e., the conduction angle of theinput signal Vin 2 is 0 degree). The input signal Vin3 is a signal witha 0˜30 degrees (0˜π/6) of phase-cut portion and a 180˜210 degrees(π˜π+π/6) of phase-cut portions (i.e., the conduction angle is 150degrees). The input signal Vin may be configured to be Vin=A2*|sin(ωt)|,wherein A2 is the amplitude of the input signal Vin and may beconfigured to be greater than, equal to or less than the amplitude A1 ofthe AC input signal Vac. Moreover, the phase-cut dimmer 110 need aprocessing time for generating the input signal Vin according to the ACinput signal Vac. For the purposes of conciseness and clear explanation,the signals Vac, Vin1, Vin2 and Vin3 are shown in FIG. 2 withoutillustrating the processing time of the phase-cut dimmer 110. In thedescription and the claims, when a signal is referred to be phase-cut,it means the voltage or the current of the signal is equal to zero or asmall signal value.

In this embodiment, one side of the transformer 120 is coupled betweenthe phase-cut dimmer 110 and the current switch 150, and the other sideof the transformer 120 is coupled between a predetermined voltage level(e.g., the ground) and the LEDs 130. The transformer 120 may beconfigured to generate the required output voltage Vout according to theinput signal Vin and the conduction status of the current switch 150.The output voltage Vout is supplied to the LEDs 130 for illuminating theLEDs 130.

The LEDs 130 are coupled between the transformer 120 and a predeterminedvoltage level (e.g., the ground). The LEDs 130 may be realized by one ormore LED packages each comprising one or more LED dies for generatingthe required brightness.

The voltage dividing circuit 140 is coupled with the phase-cut dimmer110 and a predetermined voltage level (e.g., the ground), and comprisesresistors 141 and 142 to generate a voltage dividing signal Vd at asuitable voltage level for transmitting to the LED control device 170.In other embodiments, the voltage dividing circuit 140 may be realizedwith other suitable active circuit elements and/or passive circuitelements for generating the voltage dividing signal Vd at a suitablevoltage level.

One terminal of the current switch 150 is coupled with the transformer120, and the other terminal of the current switch 150 is coupled with apredetermined voltage level (e.g., the ground) through the resistor 160.The control terminal of the current switch 150 is coupled with the LEDcontrol device 170. The current switch 150 may be realized with one ormore FETs, BJTs, other suitable type of transistors and/or othersuitable type of switch elements. The current switch 150 may beconfigured to be conducted or not conducted according to theconfiguration of the LED control device 170 so that the input signal Vinmay cause a current flowing through the transformer 120 and the currentswitch 150. The transformer 120 may generate an output current Ioutaccordingly for supplying to the LEDs 130. Moreover, when the currentIin flows through the resistor 160, a detection voltage signal Vcs maybe detected at a terminal of the resistor 160.

The LED control device 170 is coupled with the voltage dividing circuit140, the current switch 150 and the resistor 160. In this embodiment,the LED control device 170 further comprise a current control circuit171, a driving signal generating circuit 172 and a phase-cut detectioncircuit 173.

The current control circuit 171 receives the detection voltage signalVcs, and generates an output signal according to the detection voltagesignal Vcs so that the driving signal generating circuit 172 maygenerate the required driving signal accordingly.

The driving signal generating circuit 172 may be configured to generatethe driving signal for transmitting to the control terminal of thecurrent switch 150 (e.g., the gate terminal of the FET or the baseterminal of the BJT). Therefore, the current switch 150 may beconfigured to be conducted or not conducted at the suitable time so thatthe transformer 120 may generate the require output signal Vout and therequired output current Iout according to the input signal Vin.

The voltage dividing circuit 150 may generate the voltage dividingsignal Vd by scaling the input signal Vin to the suitable signal level,and the voltage dividing signal Vd may therefore be utilized todetermine whether the input signal Vin is phase-cut. In this embodiment,the phase-cut detection circuit 173 receives the voltage dividing signalVd from the voltage dividing circuit 140 for determining whether theinput signal Vin is phase-cut. Therefore, the phase-cut detectioncircuit 173 may generate one or more suitable control signals forconfiguring the current control circuit 171 to operate in the suitablemode.

FIG. 3 shows a simplified functional block diagram of the LED controldevice 170 of the phase-cut dimming system 100 in FIG. 1 according toone embodiment of the present disclosure. FIG. 4 shows simplifiedwaveforms of several signals of the phase-cut dimming system 100 inFIG. 1. The operations of the phase-cut dimming system 100 are furtherexplained below with FIGS. 3 and 4. For the purpose of conciseness andclear explanation, some components, signals and connections thereof arenot shown in FIG. 3

The current control circuit 171 comprises a signal processing circuit310, a comparator circuit 320, switches 330 and 340 and storage devices350 and 360.

The signal processing circuit 310 may be configured to generate a firstoutput signal Vo1 according to the detection voltage signals Vcsreceived in a predetermined period. For example, the signal processingcircuit 310 may generate the first output signal Vo1 according to anaverage value, an accumulated value or other suitable computation valuesof the detection voltage signals Vcs received in the period T1 in FIG.4.

In one embodiment, the signal processing circuit 310 may be realizedwith a low pass filtering circuit, which comprises one or moreresistors, inductors, capacitors, active circuit elements and/or passiveelements. The low pass filter may filter the detection voltage signalsVcs received in the predetermined period to generate the average valueof the detection voltage signals Vcs. In another embodiment, the signalprocess circuit 310 may be realized with the integrator circuitcomprising one or more amplifiers, the integrator circuit comprising theswitched capacitor circuit or the integrator circuit comprising one ormore resistors, inductors, capacitors, active circuit elements and/orpassive elements. The integrator circuit may accumulate the detectionvoltage signals Vcs received in the predetermined period to generate theaccumulated value of the detection voltage signals Vcs.

In the period T1 in FIG. 4, the control signal SW of the switch 330 isactive (high voltage level in this embodiment) and the switch 330 isconfigured to be conducted. The first output signal Vo1 of the signalprocessing circuit 310 is transmitted to an input terminal of thecomparator circuit 320 and the storage device 350. Therefore, thevoltage Vinv at the input terminal of the comparator circuit 320 and thestorage device 350 varies with the first output signal Vo1 of the signalprocessing circuit 310 in the period T1.

In the period T2 in FIG. 4, the control signal SW of the switch 330 isinactive (low voltage level in this embodiment) and the switch 330 isconfigured to be not conducted. The impedance at the input terminal ofthe comparator circuit 320 is usually high. The voltage signal Vinv atthe storage device 350 does not easily vary because a current does noteasily flow to the input terminal of the comparator circuit 320.Therefore, the voltage Vinv at the input terminal of the comparatorcircuit 320 and the storage device 350 does not vary with the firstoutput signal Vo1 of the signal processing circuit 310 in the period T2.

In the period T3 in FIG. 4, the control signal SW of the switch 330 isactive (high voltage level in this embodiment) again and the switch 330is configured to be conducted. The first output signal Vo1 of the signalprocessing circuit 310 is transmitted to the input terminal of thecomparator circuit 320 and the storage device 350. Therefore, thevoltage Vinv at the input terminal of the comparator circuit 320 and thestorage device 350 varies with the first output signal Vo1 of the signalprocessing circuit 310 again in the period T3.

The comparator circuit 320 may be configured to generate a second outputsignal Vo2 by comparing the voltage signal Vinv and a predeterminedvoltage signal Vref. The second output signal Vo2 is transmitted to thedriving signal generating circuit 172 so that the driving signalgenerating circuit 172 may generate the driving signal PWM accordingly.For example, in one embodiment, when the reference voltage signal Vrefis greater than the voltage signal Vinv, the second output signal Vo2generated by the comparator circuit 320 is equal to K*(Vref−Vinv),wherein K is configured to be a suitable value.

In the period T1 in FIG. 4, the control signal SW of the switch 340 isactive (high voltage level in this embodiment) and the switch 340 isconfigured to be conducted. The second output signal Vo2 of thecomparator circuit 320 is transmitted to an input terminal of thecomparator circuit 380 of the driving signal generating circuit 172 andthe storage device 360. Therefore, the voltage Vcmp at the inputterminal of the comparator circuit 380 of the driving signal generatingcircuit 172 and the storage device 360 varies with the second outputsignal Vo2 of the comparator circuit 320 in the period T1.

In the period T2 in FIG. 4, the control signal SW of the switch 340 isinactive (low voltage level in this embodiment) and the switch 340 isconfigured to be not conducted. The impedance at the input terminal ofthe comparator circuit 380 is usually high. The voltage signal Vcmp atthe storage device 360 does not easily vary because the current does noteasily flow to the input terminal of the comparator circuit 380 of thedriving signal generating circuit 172. Therefore, the voltage Vcmp atthe input terminal of the comparator circuit 380 of the driving signalgenerating circuit 172 and the storage device 360 does not vary with thesecond output signal Vo2 of the comparator circuit 320 in the period T2.

In the period T3 in FIG. 4, the control signal SW of the switch 340 isactive (high voltage level in this embodiment) and the switch 340 isconfigured to be conducted. The second output signal Vo2 of thecomparator circuit 320 is transmitted to the input terminal of thecomparator circuit 380 of the driving signal generating circuit 172 andthe storage device 360. Therefore, the voltage Vcmp at the inputterminal of the comparator circuit 380 of the driving signal generatingcircuit 172 and the storage device 360 varies with the second outputsignal Vo2 of the comparator circuit 320 again in the period T3.

The switches 330 and 340 are configured to be conducted or not conductedaccording to the control signal SW generated by the phase-cut detectioncircuit 173. In this embodiment, when the control signal SW is active(e.g., high voltage level in the active high signaling representation),the switches 330 and 340 are configured to be conducted. When thecontrol signal SW is inactive (e.g., low voltage level in the activehigh signaling representation), the switches 330 and 340 are configuredto be not conducted. In other embodiments, the switches 330 and 340 maybe simultaneously or not simultaneously configured according to one ormore control signals.

The storage devices 350 and 360 may be realized with capacitors,registers or other suitable memory units. When the switches 330 and 340are conducted, the signal values of the storage devices 350 and 360respectively vary with the first output signal Vo1 of the signalprocessing circuit 310 and the second output signal Vo2 of thecomparator circuit 320. When the switches 330 and 340 are not conducted,the storage device 350 and 350 are configured to keep the signal value.

In this embodiment, the driving signal generating circuit 172 generatesthe pulse width modulated signal PWM for configuring the conductionstatus of the current switch 150. The driving signal generating circuit172 comprises a ramp signal generating circuit 370 and a comparatorcircuit 380.

The ramp signal generating circuit 370 may be realized with theoscillating circuit, active circuit elements and/or passive circuitelements to generate ramp signals for transmitting to the input terminalof the comparator circuit 380. In other embodiments, the ramp signalgenerating circuit 370 may be replaced by other periodic signalgenerating circuit to generate periodic signals for transmitting to thecomparator circuit 380.

The comparator circuit 380 generates the pulse width modulated signalPWM by comparing the voltage signal Vcmp and the ramp signal generatedby the ramp signal generating circuit 370. For example, when the voltagesignal Vcmp is greater than the ramp signal, the comparator circuit 380configures the pulse width modulated signal PWM to be in the highvoltage level. When the voltage signal Vcmp is less than the rampsignal, the comparator circuit 380 configures the pulse width modulatedsignal PWM to be in the low voltage level.

The phase-cut detection circuit 173 comprises a comparator circuit 390.The comparator circuit 390 compares the voltage dividing signal Vd and areference voltage signal Vpc to determine whether the input signal Vinis phase-cut and to generate the corresponding control signal SW. Thereference voltage signal Vpc may be configured to be zero or a valueslightly greater than zero (e.g., 0.1 volt or other suitable signalvalue).

In the period T1 in FIG. 4, when the voltage dividing signal Vd isgreater than the reference voltage signal Vpc, the phase-cut detectioncircuit 173 determines the input signal Vin is not phase-cut.Accordingly, the phase-cut detection circuit 173 configures the controlsignal SW to be active so that the switches 330 and 340 becomeconducted. The first output signal Vo1 of the signal processing circuit310 is transmitted to the input terminal of the comparator circuit 320and the storage device 350. The second output signal Vo2 of thecomparator circuit 320 is transmitted to the input terminal of thedriving signal generating circuit 172 and the storage device 360. Thus,in the period T1, the voltage signal Vinv of the storage device 350 andthe voltage signal Vcmp of the storage device 360 respectively vary withthe first output signal Vo1 of the signal processing circuit 310 and thesecond output signal Vo2 of the comparator circuit 320.

In practical implementation, the signal transmission and the signalprocessing take time. Therefore, even when the input signal Vin isphase-cut in the period T1, the phase-cut detection circuit 173 cannotdetect it until the period T2 in FIG. 4. In the period T2 in FIG. 4, thevoltage dividing signal Vd is less than the reference voltage signal Vpcso that the phase-cut detection circuit 173 determines the input signalVin is phase-cut. The phase-cut detection circuit 173 configures thecontrol signal SW to be inactive so that the switches 330 and 340 arenot conducted. In the period T2, the storage devices 350 and 360respectively keep their own signal values.

In the period T3 in FIG. 4, when the voltage dividing signal Vd isgreater than the reference voltage signal Vpc, the phase-cut detectioncircuit 173 determines the input signal Vin is not phase-cut.Accordingly, the phase-cut detection circuit 173 configures the controlsignal SW to be active so that the switches 330 and 340 becomeconducted. The first output signal Vo1 of the signal processing circuit310 is transmitted to the input terminal of the comparator circuit 320and the storage device 350. The second output signal Vo2 of thecomparator circuit 320 is transmitted to the input terminal of thedriving signal generating circuit 172 and the storage device 360. Thus,in the period T3, the voltage signal Vinv of the storage device 350starts from the signal value kept in the period T2 and varies with thefirst output signal Vo1 of the signal processing circuit 310. Thevoltage signal Vcmp of the storage device 360 starts from the signalvalue kept in the period T2 and varies with the second output signal Vo2of the comparator circuit 320.

When the input signal Vin is phase-cut (e.g., in the period T2 in FIG.4), the phase-cut detection circuit 173 configures the control signal SWto be inactive so that the switches 330 and 340 are not conducted. Thestorage devices 350 and 360 respectively keep their own signal value sothat the voltage signal Vinv at the input terminal of the comparatorcircuit 320 and the voltage signal Vcmp at the input terminal of thecomparator circuit 380 do not vary substantially.

When the input signal Vin is no longer phase-cut (e.g., in the period T3in FIG. 4), the phase-cut detection circuit 173 configures the controlsignal SW to be active so that the switches 330 and 340 are conducted.The signal values of the storage devices 350 and 360 are kept atsubstantially the same value before the input signal Vin was phase-cut.The comparator circuits 320 and 380 may rapidly resume to the operationstatuses (e.g., the operation statuses in operation T1 in FIG. 4)according to the signal values kept in the storage devices 350 and 360.Accordingly, a suitable pulse width modulated signal PWM may begenerated to configure the conduction status of the current switch 150.The transformer 120 may therefore supply the required output voltageVout and/or the required output current Iout to the LEDs 130 so as toobtain the required dimming effect.

In the above embodiments, the storage devices 350 and 360 may beconfigured to keep the signal values. Therefore, the comparator circuit320 and 380 may operate in the similar operation status before and afterthe input signal Vin is phase-cut to prevent the LEDs 130 fromflickering.

Because the current Iin is caused by applying the input signal Vin onthe transformer 120 and the current switch 150, the waveforms of thecurrent Iin and the input signal Vin are similar. When the input signalVin is phase-cut, the current Iin therefore becomes zero or a very smallvalue. Therefore, in other embodiments, the LED control device 170 mayalso detect whether the input signal Vin is phase-cut according to thedetection voltage signal Vcs, which is generated by flowing the currentIin through the resistor 160.

FIG. 5 shows a simplified functional block diagram of a phase-cutdimming system 500 according to another embodiment of the presentdisclosure. The phase-cut dimming system 500 comprises a phase-cutdimmer 110, a transformer 120, a group of LEDs 130, a voltage dividingcircuit 140, a current switch 150, a resistor 160 and a LED controldevice 170. For the purposes of conciseness and clear explanation, somecomponents, signals and connections thereof are not shown in FIG. 5.

The implementations, the operations and the description of thecomponents in the dimmer system 100 may be applicable to the dimmersystem 500. One difference, however, between the dimmer system 500 andthe dimmer system 100 is that the LED control device 170 of the dimmersystem 500 detects whether the input signal Vin is phase-cut accordingto the detection voltage signal Vcs and generates control signals forconfiguring the operation of the current control circuit 171. In theembodiment in FIG. 5, although the LED control device 170 still receivesthe voltage dividing signal Vd, the voltage dividing signal Vd isutilized by other circuits (not shown in FIG. 5).

FIG. 6 shows a simplified functional block diagram of the LED controldevice 170 of the phase-cut dimming system 500 in FIG. 5 according toone embodiment of the present disclosure. In the embodiment in FIG. 6,the comparator circuit 390 determines whether the input signal Vin isphase-cut by comparing the detection voltage signal Vcs and thereference voltage signal Vpc1 and generates the corresponding controlsignal SW. The reference voltage signals Vpc and Vpc1 may be configuredto be the same or different according to different designconsiderations. The implementations, the operations and the descriptionof the components in the LED control device 170 in FIG. 3 may beapplicable to the embodiment in FIG. 6, and not repeated here for thepurpose of conciseness.

In the above embodiments, the dimmer systems with the flyback regulatorare utilized to explanation. In other embodiment, the dimmer systemswith other types of regulators may also be applicable, e.g., the boosttype regulator and the buck type regulator.

FIG. 7 shows a simplified functional block diagram of a phase-cutdimming system 700 according to another embodiment of the presentdisclosure. The phase-cut dimming system 700 comprises a phase-cutdimmer 110, an inductor 720, a group of LEDs 130, a voltage dividingcircuit 140, a current switch 150, a resistor 160 and a LED controldevice 170. For the purposes of conciseness and clear explanation, somecomponents, signals and connections thereof are not shown in FIG. 7. Theimplementations, the operations and the description of the components inthe above dimmer systems may be applicable to the dimmer system 700, andnot repeated here for the purpose of conciseness.

Similar to the embodiment in FIG. 1, the LED control device 170 iscoupled with the voltage dividing circuit 140, the current switch 150and the resistor 160. The LED control device 170 comprises a currentcontrol circuit 171, a driving signal generating circuit 172 and aphase-cut detection circuit 173. The control circuit 170 may detectwhether the input signal Vin is phase-cut according to the voltagedividing signal Vd, and generate control signals for configuring thecurrent control circuit to operation in the required status. When theinput signal Vin is phase-cut, the LED control device 170 stores thesignal values of the internal circuits in the storage devices. When theinput signal is no longer phase-cut, the LED control device 170 mayrapidly resume to the previous operation status according to the storedsignal values. Therefore the LED control device 170 may configure theoutput current Iout more precisely according to the configuration of thephase-cut dimmer 110. In another embodiment, the LED control device 170may be realized with the embodiments in FIGS. 5 and 6 to detect whetherthe input signal Vin is phase-cut according to the detection voltagesignal Vcs.

In the above embodiment, the dimmer systems may cooperate with differenttypes of regulator according to different design considerations andperform the required dimming function of the LEDs 130.

In the above embodiments, the LED control device 170 detects whether theinput signal Vin is phase-cut according to only one of the voltagedividing signal Vd and the detection voltage signal Vcs. In anotherembodiment, the LED control device 170 may detect whether the inputsignal Vin is phase-cut according to both the voltage dividing signal Vdand the detection voltage signal Vcs. For example, the phase-cutdetection circuit 173 compares the voltage dividing signal Vd and thedetection voltage signal Vcs respectively with the reference voltagesignals Vpc and Vpc1. When the voltage dividing signal Vd is less thanthe reference voltage signal Vpc and/or the detection voltage signal Vcsis less than the reference voltage signal Vpc1, the phase-cut detectioncircuit 173 determines the input signal Vin is phase-cut.

In the above embodiments, each functional block may be realized withanalog circuits and/or digital circuits. For example, in one embodiment,the signal processing circuit 310 and the comparator circuit 320 arerealized with analog circuits and the storage devices 350 and 360 arerespectively realized with one or more capacitors. When the storagedevices 350 and 360 are realized with capacitors, the signal values ofthe storage devices 350 and 360 may still slightly vary because of thecapacitor leakage current even if the switches 350 and 360 are notconducted. For example, when the frequency of the AC input signal Vac is60 Hz and the storage devices 350 and 360 are realized with capacitors,the stored voltage signals Vinv and Vcmp may decade less than 100 mV inthe period T2 in FIG. 4.

In another embodiment, the signal processing circuit 310 and thecomparator circuit 320 are realized with digital circuits. The signalprocessing circuit 310 further comprises an analog to digital convertingcircuit to convert the analog detection voltage signal Vcs into thedigital representation for further signal processing. In thisembodiment, the storage devices 350 and 360 may be realized withregisters for storing the digital output signals of the signalprocessing circuit 310 and the comparator circuit 320. In thisembodiment, the signal values stored in the storage 350 and 360 do notdecade.

In another embodiment, the storage device 350 and 360 may start to varyrespectively with the output signals Vo1 and Vo2 of the signalprocessing circuit 310 and the comparator circuit 320 according to thecontrol signals generated by the phase-cut detection circuit 173. Forexample, the phase-cut detection circuit 173 may configure the storagedevices 350 and 360 start to vary with the output signals Vo1 and Vo2 ata predetermined period after the input signal Vin is no longerphase-cut.

In another embodiment, the LED control device 170 may be realized withonly one of the storage devices 350 and 360. In another embodiment,other circuits of the LED control device 170 may utilize the storagedevices to store the signal values before the input signal Vin isphase-cut, and may rapidly resume to the previous operation statusaccording to the stored signal values after input signal Vin is nolonger phase-cut.

In another embodiment, to further reduce the power consumption, thedriving signal generating circuit 172 may stop generating the pulsewidth modulated signal PWM when the input signal Vin is phase-cutaccording to the control signal of the phase-cut detection circuit 173.

In the embodiments above, the LED control device 170 may also normallyfunction and supply the required voltage and/or the required current tothe LEDs 130 when the input signal Vin is not phase-cut (i.e., theconduction angle is 180 degrees).

In the above embodiments, each functional block may be respectivelyrealized with one or more circuit elements. Multiple functional blocksmay also be integrated into one circuit element. For example, thestorage devices 350 and 360 may be respectively configured in theinterior or the exterior of the LED control device 170. In anotherembodiment, the current switch 150 may be integrated in the LED controldevice 170 so that the number of discrete circuit elements and thehardware complexity may be reduced.

In the above embodiments, the LED control device 170 may perform thedimming function by detecting whether the input signal Vin is phase-cut.Thus, even if the conduction angle of the input signal Vin is close to180 degrees, the LED control device 170 may still correctly perform thedimming function. The LED control device 170 may perform the dimmingfunction in a wider range of conduction angle so that the user mayeasily configure the LEDs 130 to the required brightness.

In the above embodiments, when the input signal Vin is phase-cut, theLED control device 170 stores the signal values of the internal circuitsto the storage devices. When the input signal Vin is no longerphase-cut, the LED control device 170 may rapidly resume to theoperation status before the input signal Vin is phase-cut according tothe stored signal values. Thus, the LED control device 170 may configurethe output current Iout supplied to the LEDs 130 more preciselyaccording to the configuration of the phase-cut dimmer 110. Thelinearity of the phase-cut dimming system may be improved and the usermay easily configure the LEDs to the required brightness.

In the above embodiments, the voltage dividing signal Vd and thedetection voltage signal Vcs are commonly utilized in the power factorcorrection circuit. Therefore, the LED control device 170 may be easilyintegrated in the power factor correction circuit without occupyingadditional package pins. The functions of constant output current, powerfactor correction, LED driving and dimming may be integrated in a singleintegrated circuit for further reducing the hardware complexity.

In the drawings, the waveforms of some signals may be simplified orexaggerated for clear explanation, and the size and relative sizes ofsome elements may be exaggerated or simplified for clarity. Accordingly,unless the context clearly specifies, the shape, size, relative size,and relative position of each element in the drawings are illustratedmerely for clarity, and not intended to be used to restrict the claimscope.

Certain terms are used throughout the description and the claims torefer to particular components. One skilled in the art appreciates thata component may be referred to as different names. This disclosure doesnot intend to distinguish between components that differ in name but notin function. In the description and in the claims, the term “comprise”is used in an open-ended fashion, and thus should be interpreted to mean“include, but not limited to.” The phrases “be coupled with,” “coupleswith,” and “coupling with” are intended to compass any indirect ordirect connection. Accordingly, if this disclosure mentioned that afirst device is coupled with a second device, it means that the firstdevice may be directly or indirectly connected to the second devicethrough electrical connections, wireless communications, opticalcommunications, or other signal connections with/without otherintermediate devices or connection means.

The term “and/or” may comprise any and all combinations of one or moreof the associated listed items. In addition, the singular forms “a,”“an,” and “the” herein are intended to comprise the plural forms aswell, unless the context clearly indicates otherwise.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention indicated by the following claims.

What is claimed is:
 1. An LED control device for configuring a phase-cutdimming system according to an input signal; wherein the phase-cutdimming system comprises an LED and a current switch; comprising: acurrent control circuit for coupling with the current switch, and forgenerating a second output signal according to a current flowing throughthe current switch; a driving signal generating circuit for couplingwith a control terminal of the current switch and the current controlcircuit, and for generating a driving signal to configure a conductionstatus of the current switch according to the second output signal and aperiodic signal; and a phase-cut detection circuit for receiving theinput signal, and for comparing the input signal with a second referencesignal; wherein in a first period in which the input signal is greaterthan the second reference signal, the phase-cut detection circuitconfigures a signal value of a second storage device to vary with thesecond output signal; in a second period in which the input signal isless than the second reference signal, the phase-cut detection circuitconfigures the second storage device to keep the signal value of thesecond storage device so as not to vary with the second output signal;in a third period in which the input signal is greater than the secondreference signal, the phase-cut detection circuit configures the signalvalue of the second storage device to vary with the second outputsignal; and the second storage device is configured to be operablycoupled with the current control circuit and the driving signalgenerating circuit, and wherein the current control circuit generates afirst output signal according to the current flowing through the currentswitch and generates the second output signal according to the firstoutput signal and a first reference signal; in the first period, thephase-cut detection circuit configures a signal value of a first storagedevice to vary with the first output signal; in the second period, thephase-cut detection circuit configures the first storage device to keepthe signal value of the first storage device so as not to vary with thefirst output signal; in the third period, the phase-cut detectioncircuit configures the signal value of the first storage device to varywith the first output signal; the first storage device is configured tobe operably coupled with the current control circuit; and the firststorage device is configured to be in at least one of the interior ofthe LED control device and the exterior of the LED control device. 2.The LED control device of claim 1, wherein in the third period, thedriving signal generating circuit generates the driving signal accordingto the second output signal, the signal value of the second storagedevice and the periodic signal.
 3. The LED control device of claim 2,further comprising: a second switch coupled between the current controlcircuit and the second storage device; wherein when the phase-cutdetection circuit configures the second switch to be not conducted, thesignal value of the second storage device does not vary with the secondoutput signal.
 4. The LED control device of claim 1, wherein in thethird period, the current control circuit generates the second outputsignal according to the first output signal, the signal of the firststorage device and the first reference signal.
 5. The LED control deviceof claim 4, further comprising: a first switch coupled between thecurrent control circuit and the first storage device; wherein when thephase-cut detection circuit configures the first switch to be notconducted, the signal value of the first storage device does not varywith the first output signal.
 6. The LED control device of claim 4,wherein the current control circuit generates the first output signalaccording to at least one of an average value and an accumulated valueof the current flowing through the current switch.
 7. An LED controldevice for configuring a phase-cut dimming system according to an inputsignal; wherein the phase-cut dimming system comprises an LED and acurrent switch, and a current flowing through the current switch flowsthrough a resistor to generate a detection voltage signal; comprising: acurrent control circuit for coupling with the current switch, and forgenerating a second output signal according to the current flowingthrough the current switch; a driving signal generating circuit forcoupling with a control terminal of the current switch and the currentcontrol circuit, and for generating a driving signal to configure aconduction status of the current switch according to the second outputsignal and a periodic signal; and a phase-cut detection circuit forreceiving the detection voltage signal, and for comparing the detectionvoltage signal with a third reference signal; wherein in a first periodin which the detection voltage signal is greater than the thirdreference signal, the phase-cut detection circuit configures a signalvalue of a second storage device to vary with the second output signal;in a second period in which the detection voltage signal is less thanthe third reference signal, the phase-cut detection circuit configuresthe second storage device to keep the signal value of the second storagedevice so as not to vary with the second output signal; in a thirdperiod in which the detection voltage signal is greater than the thirdreference signal, the phase-cut detection circuit configures the signalvalue of a second storage device to vary with the second output signal;and the second storage device is configured to be operably coupled withthe current control circuit and the driving signal generating circuit,and wherein the current control circuit generates a first output signalaccording to the current flowing through the current switch andgenerates the second output signal according to the first output signaland a first reference signal; in the first period, the phase-cutdetection circuit configures a signal value of a first storage device tovary with the first output signal; in the second period, the phase-cutdetection circuit configures the first storage device to keep the signalvalue of the first storage device so as not to vary with the firstoutput signal; in the third period, the phase-cut detection circuitconfigures the signal value of the first storage device to vary with thefirst output signal; the first storage device is configured to beoperably coupled with the current control circuit; and the first storagedevice is configured to be in at least one of the interior of the LEDcontrol device and the exterior of the LED control device.
 8. The LEDcontrol device of claim 7, wherein in the third period, the drivingsignal generating circuit generates the driving signal according to thesecond output signal, the signal value of the second storage device andthe periodic signal.
 9. The LED control device of claim 8, furthercomprising: a second switch coupled between the current control circuitand the second storage device; wherein when the phase-cut detectioncircuit configures the second switch to be not conducted, the signalvalue of the second storage device does not vary with the second outputsignal.
 10. The LED control device of claim 7, wherein in the thirdperiod, the current control circuit generates the second output signalaccording to the first output signal, the signal of the first storagedevice and the first reference signal.
 11. The LED control device ofclaim 10, further comprising: a first switch coupled between the currentcontrol circuit and the first storage device; wherein when the phase-cutdetection circuit configures the first switch to be not conducted, thesignal value of the first storage device does not vary with the firstoutput signal.
 12. The LED control device of claim 10, wherein thecurrent control circuit generates the first output signal according toat least one of an average value and an accumulated value of the currentflowing through the current switch.